Electrode for electrolytic capacitor, electrolytic capacitor, and manufacturing method therefor

ABSTRACT

An electrode for electrolytic capacitors having a large capacitance and having excellent tan δ, heat resistance, humidity resistance and stability. An electrolytic capacitor using the electrode. An electrode obtained by attaching a compound having a siloxane bond onto the surface of an electrode body comprising a valve-acting metal having formed thereon a dielectric film. The compound having a siloxane bond is attached by coating, dipping or vapor deposition. A solid electrolytic capacitor obtained by forming an electrolyte comprising an electrically conducting polymer on the electrode.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/262,613, which is adivisional of application Ser. No. 09/598,914 filed Jun. 22, 2000, whichclaims benefit of Provisional Application No. 60/141,248 filed Jun. 30,1999; the above noted prior applications are all hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to an electrode for electrolyticcapacitors, an electrolytic capacitor using the electrode, and amanufacturing method therefor.

BACKGROUND OF THE INVENTION

To keep up with the recent trend toward reduction in the size and theweight of electronic equipment, a compact capacitor showing lowimpedance in the high frequency region and having a large capacitance isdemanded. As a capacitor for use at high frequency, mica capacitor, filmcapacitor, ceramic capacitor and the like have been heretofore used.These capacitors are, however, not suitable for achieving a largecapacitance. As a compact capacitor having a large capacitance, aluminumelectrolytic capacitor and tantalum electrolytic capacitor are generallyused.

The electrolyte used in these electrolytic capacitors is a liquidelectrolyte or a solid manganese dioxide. In recent years, a capacitorwhere a TCNQ (7,7,8,8-tetracyanoquinodimethane) complex salt, which isan organic semiconductor, is used as the solid electrolyte has beenproposed.

This capacitor is disadvantageous in that although the TCNQ complex saltis heated/melted, impregnated into an electrode and cooled/solidified toform a solid electrolyte, the TCNQ complex salt is likely to decomposeand deteriorate at the melting temperature. Therefore, the productionprocess thereof becomes very complicated and the cost increases.

In order to solve these problems, use of a solid electrolyte comprisinga polymer of 5-membered heterocyclic compound having an electricalconductivity higher than the manganese dioxide or TCNQ complex salt,such as pyrroles, thiophenes and furans, have been proposed. A solidelectrolytic capacitor using such an electrically conducting polymer hassuperior frequency properties compared with electrolytic capacitorsusing an electrolytic solution, because the electrically conductingpolymer exhibits high electrical conductivity.

With respect to the surface treatment of electrochemically formed film(dielectric film) of the electrode, a method of allowing silicic acid orsilicate to be present on the film surface to prevent deterioration inthe capacitance and dielectric loss at high temperature and highhumidity is known (see, JP-A-5-234821 (the term “JP-A” as used hereinmeans an “unexamined published Japanese patent application”) andJP-A-5-234822). However, this method is problematic with respect tohumidity resistance.

Also, a solid electrolytic capacitor using a valve-acting metal havingformed thereon a dielectric layer after surface treating thevalve-acting metal by impregnating it with a silane coupling agentsolution is known (JP-A-2-74021). The silane coupling agent is used inthe form of an aqueous solution, and silanol is produced afterhydrolysis and reacts by condensation with the hydroxyl group of thedielectric film to form a covalent bond. Therefore, heating isnecessary. Furthermore, a thin film capacitor which is surface treatedby dipping it in a solution of chlorosilane-based surfactant containinga fluorinated carbon chain (see, JP-A-4-36721) is known. In thistechnique, the chemical reaction group of the silane compound chemicallybonds to the hydroxyl group of the dielectric film in a non-aqueoussolvent system, and surface modification can be attained. However, HClmay be side produced to damage the dielectric film, and the reagent isexpensive and readily reacts with water. As a result, this method isproblematic with respect to profitability and stability of the reagent.

In the case of a solid electrolytic capacitor where the dielectric filmon the valve-acting metal is an inorganic material and the electrolyteformed on the film is an electrically conducting polymer of an organicmaterial, adhesion between the electrically conducting polymer and thedielectric film is weak and separation therebetween takes place veryoften at high temperatures. Accordingly, the capacitancedisadvantageously decreases with time.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrode suitablefor electrolytic capacitors, preferably electrolytic capacitors using anelectrically conducting polymer for the electrode, where theelectrolytic capacitor has a large capacitance and high stability athigh temperatures.

The present invention has been made to solve the above-describedproblems and fundamentally provides the following embodiments:

(1) an electrode for an electrolytic capacitor, obtained by attaching acompound having a siloxane bond onto an electrode comprising avalve-acting metal having on the surface thereof a porous dielectricfilm;

(2) a method for manufacturing an electrode for an electrolyticcapacitor, comprising dipping an electrode comprising a valve-actingmetal having on the surface thereof a porous dielectric film in asolution of a compound having a siloxane bond, or coating the solutionon the electrode;

(3) a method for manufacturing an electrolytic capacitor, comprisingexposing an electrode comprising a valve-acting metal having on thesurface thereof a porous dielectric film to an atmosphere of a compoundhaving a siloxane bond to attach said compound to the surface of theelectrode;

(4) a solid electrolytic capacitor obtained by forming an electrolytecomprising an electrically conducting polymer on an electrode describedin (1) above; and

(5) a method for manufacturing an electrolytic capacitor, comprisingattaching a compound having a siloxane bond onto a dielectric film of anelectrode, comprising a valve-acting metal having on the surface thereofa porous dielectric film, with the end part thereof undertaking theanode part, forming in sequence an electrode on the dielectric film andfurther thereon an electrically conducting layer, thereby fabricating acapacitor device using these members as the cathode part, and connectinga lead frame to the anode part and the cathode part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing one example of the electrolyticcapacitor of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electrode for electrolytic capacitors of the present invention ischaracterized in that a compound having a siloxane bond is attached toan electrode comprising a valve-acting metal having formed thereon adielectric film. The electrode is suitably used for a solid electrolyticcapacitor but may also be used for electrolytic capacitors using aliquid electrolyte.

The valve-acting metal used is a valve-acting metal such as aluminum,titanium, tantalum, niobium or an alloy mainly comprising one or more ofthese metals. The, shape thereof may be any of foil, plate and bar. Inthe case of tantalum and/or niobium or an alloy thereof, the powderthereof may be molded and sintered.

The valve-acting metal is subjected to an etching or electrochemicallyforming treatment by a known method so as to form a dielectric layer onthe valve-acting metal and increase the specific surface area.

Onto this dielectric film, a compound having a siloxane bond(hereinafter referred to as a “siloxane compound”) is attached. Thesiloxane compound readily forms an intermolecular hydrogen bond betweenthe siloxane bond in the molecule and the hydroxyl group on the oxidesurface on the dielectric film, has affinity, and is maintained toadhere to the dielectric film. The present invention utilizes theseproperties. Accordingly, the siloxane compound may be any compound aslong as it contains a siloxane bond. However, a low molecular weightsiloxane (a cyclic or linear compound having a weight average molecularweight of 100,000 or less) is preferred. Examples of the siloxanecompound product which can be used include silicone oil, siliconerubber, silicone resin and silicon varnish.

Trade names of siloxane compounds are specifically described below.

Cyclic Siloxane

KF 994 and KF 995 produced by Shin-Etsu Chemical Co., Ltd.; and SIO6705, SIT 7530, SIT 7900, SIT 8737, SID 4625 and SIH 6105 produced byGelest Inc.

Organic Modified Silicone Oil

-   (1) Alkyl silicone oil

KF 96, KF 69 and KF 54 produced by Shin-Etsu Chemical Co., Ltd.

-   (2) Fluorosilicone oil

FMS-123 produced by Gelest Inc.

-   (3) Polyalkylene oxide-modified silicone

DBE-712 produced by Gelest Inc.

-   (4) Hydroxy or Cation-type silicone

CMS G26 produced by Gelest Inc. and KF 99 produced by Shin-Etsu ChemicalCo., Ltd.

-   (5) Silanol silicone

DMS-S12 produced by Gelest Inc.

Non-Reactive Silicone Oil

KF 352 and KF 6012 as polyether-modified silicone, KF 410 asmethylstyryl-modified silicone, KF 412 as alkyl-modified silicone, KF910 as higher fatty acid ester-modified silicone, KF 905 as hydrophilicspecial silicone, KF 851 as higher alkoxy-modified silicone, and KF 100as fluorine-modified silicone (all produced by Shin-Etsu Chemical Co.,Ltd.).

Reactive Silicone Oil

-   (1) Vinyl silicone

DMS-V00 produced by Gelest Inc.

-   (2) Amino-modified silicone

KF 393, KF 860 (both produced by Shin-Etsu Chemical Co., Ltd.), DMS-A11(produced by Gelest Inc.) and SF-8417 (produced by Dow Corning ToraySilicone Co., Ltd.).

-   (3) Epoxy-modified silicone

KF 1001, KF 102 (both produced by Shin-Etsu Chemical Co., Ltd.) andDMS-E01 (produced by Gelest Inc.).

-   (4) Carboxyl-modified silicone

X-22-3710, DMS-B12 (both produced by Gelest Inc.) and SF-8411 (producedby Dow Corning Toray Silicone Co., Ltd.).

-   (5) Carbinol-modified silicone

KF 6001 (produced by Shin-Etsu Chemical Co., Ltd.) and DMS-CIS (producedby Gelest Inc.).

-   (6) Methacryl-modified silicone

X-22-2404 and DMS-R01 (both produced by Gelest Inc.).

-   (7) Mercapto-modified silicone

X-22-980 and SMS-022 (both produced by Gelest Inc.).

When attached onto the surface of dielectric film, the siloxane compoundaccelerates the formation of an electrically conducting polymer in finepores of a dielectric film obtained by etching or the like, and exhibitsexcellent properties such as defoaming property, heat resistance,insulating property, chemical resistance and chemical stability. As aresult of the presence of the siloxane compound, the degree of adhesionbetween the dielectric film and the electrically conducting polymer canbe increased, which results in higher capacitance of the capacitor andsmaller tangent (tan δ) of the loss angle.

A first method for attaching a siloxane compound onto the dielectricfilm of an electrode is a method of coating a solution (including adispersion solution) of siloxane compound on the film or dipping theelectrode in the siloxane compound-containing solution. Examples of thesolvent for the solution include ethers such as tetrahydrofuran (THF),dioxane and diethyl ether, aprotic polar solvents such asdimethylformamide (DMF), acetonitrile, benzonitrile, N-methylpyrrolidone(NMP) and dimethylsulfoxide (DMSO), esters such as ethyl acetate andbutyl acetate, non-aromatic chlorine-based solvents such as chloroformand methylene chloride, nitro compounds such as nitromethane,nitroethane and nitrobenzene, alcohols such as methanol, ethanol andpropanol, acetone and water. In the solvent, the siloxane compound ispresent in a concentration of from about 0.0001 to 1.0 wt %, preferablyfrom about 0.001 to 0.5 wt %.

A second method for attaching a siloxane compound is a method ofexposing the electrode to an atmosphere of siloxane compound to attachthe compound onto the electrode surface. In this case, for example, whensilicone rubber is used, it converts into a siloxane compound having asilicon number shorten in the Examples. After the attachment, however,this does not cause any trouble as long as the compound has a siloxanebond.

By these methods, a siloxane compound can be substantially attached eveninto fine pores of the dielectric film. The term “substantially” as usedherein means that, for example, the amount of siloxane compound attachedto the dielectric film may be small to an extent such that the siloxanecompound can be detected in the region of about 100 Å in the depthdirection of the dielectric film layer by an X-ray photoelectronspectrum (XPS) or can be detected by an Auger electron spectrum (AES).The siloxane compound may be attached either uniformly or non-uniformly.

A solid electrolytic capacitor using the above-described electrode ofthe present invention is described below. FIG. 1 shows one example ofthe solid electrolytic capacitor of the present invention. On avalve-acting metal 1, a dielectric film 3 and fine pores 2 are formed.Onto the film, a siloxane compound 4 is attached into inside of finepores.

On the thus-constructed electrode of the present invention, anelectrically conducting polymer 5 is formed. The electrically conductingpolymer used is a polyaniline and 5-membered heterocyclic electricallyconducting polymer such as polypyrrole, polythiophene and polyfuran, orsubstituted derivatives thereof, preferablypoly(3,4-ethylenedioxythiophene). The polymerization may be eitherelectrolytic polymerization or chemical polymerization. However,chemical polymerization by adding an oxidizing agent to a solutionhaving dissolved or dispersed therein monomers constituting the polymeris preferred. The solvent used for dissolving the monomers is the sameas the above-described solvent for use in dissolving or dispersingisopropyl alcohol or siloxane compound. Examples of the oxidizing agentused for the chemical polymerization include persulfates such aspotassium persulfate, sodium persulfate and ammonium persulfate,peroxides such as hydrogen peroxide, and metal halides such as ferricchloride and aluminum chloride. Among these, ammonium persulfate ispreferred.

In the electrically conducting polymer for use in the solid electrolyticcapacitor, a dopant is generally used. Depending on the kind of dopant,the surface of the electrically conducting polymer is usually varied inthe flatness, roughness and the like. As a result, the the electricallyconducting polymer coating on the dielectric film greatly varies. Forthe electrically conducting polymer used in a solid electrolyticcapacitor, an aryl sulfonate-based dopant is generally used. When, forexample, a sodium salt of benzenesulfonic acid, toluenesulfonic acid,naphthalenesulfonic acid or anthracenesulfonic acid is used, thecovering state of the electrically conducting polymer produced on theelectrode varies among respective cases and in turn the capacitancediffers. However, by attaching a siloxane compound to the dielectricfilm, an adhesion effect is provided between the polymer and thedielectric film and thereby the difference in the covering state ofpolymer depending on the kind of dopant is reduced. As a result, auniform polymer can be obtained.

The electrically conducting polymer may be formed on the dielectric filmhaving attached thereto a siloxane compound by a method where a monomerof the electrically conducting polymer is coated on the film using themonomer alone or after dissolving or dispersing it in a solvent, or thefilm may be dipped in the monomer solution, to uniformly disperse themonomer on the dielectric film. Then the film is dipped in a solution ordispersion solution containing, for example, an oxidizing agent in anamount of from 0.01 to 2 mol/l and a dopant in an amount of from 0.01 to2 mol/l to cause chemical polymerization. The electrically conductingpolymer may also be similarly formed by chemical polymerization evenwhen (1) the coating of or dipping in the solution or dispersionsolution containing the monomer and (2) the coating of or dipping in thesolution or dispersion solution containing an oxidizing agent and adopant are performed in the reverse order or performed simultaneously inone solution. The polymerization temperature is generally from −70 to250° C., preferably from 0 to 150° C., more preferably from 0 to 100° C.

On the thus-formed electrically conducting polymer, another electricallyconducting layer is preferably provided to further improve theelectrical contact. This electrically conducting layer 6 is formedusing, for example, an electrically conducting paste layer such as knowncarbon paste and silver paste, plating, metallization or an electricallyconducting resin film. Furthermore, on this electrically conductinglayer, an outer jacket 7 is provided by resin molding, by using a resincase or metal-made case, or by resin dipping. Thereafter, a connectionterminal (anode) 8 and a connection terminal (cathode) 9 are providedthereto. Then, an electrolytic capacitor product suitable for varioususes can be manufactured. In FIG. 1, one constituent unit of theelectrolytic capacitor is shown and on actual use as a product, aplurality of the constituent units (capacitor elements) are generallystacked.

EXAMPLES

The present invention is described in greater detail below by referringto Examples and Comparative Examples. Unless otherwise indicated, allparts, percents, ratios and the like are by weight.

Example 1

A formed aluminum foil was subjected to electrochemical forming at 13 Vby dipping the foil in a 10 wt % aqueous ammonium adipate solution toform a dielectric film on the foil surface. This formed aluminum foil(substrate) was placed together with a high-temperaturevulcanization-type silicone rubber (heat resistant temperature: 250° C.)in a drier (volume: 91 l) at about 180° C. and kept for about 1 hour toattach a siloxane compound onto the film. This siloxane compound wasexamined by a gas chromatographic mass spectrometry (GC-MS) and found tohave a siloxane bond represented by the formula: [—O—SiR¹R²—]n (whereinR¹ and R² both are CH₃). The majority of the compounds were compoundswhere n is from 7 to 16. Subsequently, the formed foil was dipped in anisopropyl alcohol (hereinafter simply referred to as “IPA”) solutioncontaining 1.2 mol/l of 3,4-ethylenedioxythiophene (produced by BayerAG) and then dipped in an aqueous solution prepared to have an ammoniumpersulfate (hereinafter simply referred to as “APS”) concentration of 2mol/l and a sodium anthraquinone-2-sulfonate concentration of 0.07 wt %.

The substrate was taken out and left standing in air at about 40° C. forabout 10 minutes to allow the oxidative polymerization to proceed. Thisstep was repeated 25 times. After this polymerization reaction, thesubstrate was washed.

Thereafter, generally known carbon paste (graphite powder+epoxyresin+acetic ester as the solvent) and silver paste (silver powder+epoxyresin+the same solvent) were coated in this order on the capacitorelement (polymerization reaction area: 3×4 mm). Four sheets of capacitorelements were stacked one on another, connected on a lead frame andbonded to a cathode lead terminal. The electric current from the anodeof the elements was collected by welding the aluminum core part of thesubstrate to an electrode lead terminal. Finally, the whole was moldedwith epoxy resin to manufacture an electrolytic capacitor. Thethus-obtained capacitor was aged for 2 hours by applying thereto a ratedvoltage at 125° C. and then measured on the initial properties. In anaccelerated humidity test, the capacitor was left standing in hightemperature and high humidity conditions of 85° C. and 85% relativehumidity (RH) for 240 hours.

In Table 1, initial properties are shown, where C indicates acapacitance and DF indicates a tangent of loss angle (DF=tan δ×100%),each measured at 120 Hz. LC (leakage current) and short circuit testswere measured 1 minute after the application of rated voltage (13 V).Respective measured values were an average of 30 units of samples. Thesample was determined as defective when LC was 1 μA or more, and thesample was determined as a short circuited product when LC was 10 μA ormore. The average of LC was calculated excluding short circuitedproducts, if present. The results obtained are shown together in Table1.

Example 2

Capacitors were manufactured and evaluated in the same manner as inExample 1 except that sodium 4-morpholinepropanesulfonate was used inplace of sodium anthraquinone-2-sulfonate in Example 1. The resultsobtained are shown in Table 1.

Example 3

Capacitors were manufactured and evaluated in the same manner as inExample 1 except that sodium anthracene-1-sulfonate was used in place ofsodium anthraquinone-2-sulfonate in Example 1. The results obtained areshown in Table 1.

Example 4

Capacitors were manufactured and evaluated in the same manner as inExample 1 except that sodium 1-naphthalenesulfonate was used in place ofsodium anthraquinone-2-sulfonate and pyrrole was used in place of3,4-ethylenedioxythiophene in Example 1. The results obtained are shownin Table 1.

Example 5

The formed aluminum foil (substrate) obtained in Example 1 was placed ina drier (volume: 91 l) having charged thereinto 6 g ofoctamethylcyclotetrasiloxane (produced by Aldrich Chemical Co., Inc.)and heated at 40° C. After 5 minutes, the substrate was taken out.

Capacitors obtained through the same subsequent procedure as in Example1 were evaluated in the same manner as in Example 1. The results areshown in Table 1.

Example 6

The formed aluminum foil (substrate) obtained in Example 1 was placed ina drier (volume: 91 l) in which 6 g of hexamethylcyclotrisiloxane(produced by Gelest Inc.) was charged and allowed to stand at 20° C.After 5 minutes, the substrate was taken out.

Capacitors obtained through the same subsequent procedure as in Example1 were evaluated in the same manner as in Example 1. The results areshown in Table 1.

Example 7

The formed aluminum foil (substrate) obtained in Example 1 was dipped ina 0.1 wt % hexamethylcyclotrisiloxane solution dissolved in acetone andthen dried at 50° C. for 10 minutes. Evan after drying at thistemperature, hexamethylcyclotrisiloxane remained. It is considered thatintermolecular hydrogen bonding was generated with the dielectricmaterial.

Capacitors obtained through the same subsequent procedure as in Example1 were evaluated in the same manner as in Example 1. The results areshown in Table 1.

Example 8

The formed aluminum foil (substrate) obtained in Example 1 was dipped ina 0.001 wt % decamethylcyclopentasiloxane (produced by Chisso K. K.)solution dissolved in acetone and then dried at 50° C. for 10 minutes.

Capacitors obtained through the same subsequent procedure as in Example1 were evaluated in the same manner as in Example 1. The results areshown in Table 1.

Example 9

The formed aluminum foil (substrate) obtained in Example 1 was dipped ina 0.1 wt % dimethylsilicone oil (KF-96, trade name, produced byShin-Etsu Chemical Co., Ltd.) solution dissolved in acetone and thendried at 50° C. for 10 minutes.

Capacitors obtained through the same subsequent procedure as in Example1 were evaluated in the same manner as in Example 1. The results areshown in Table 1.

Comparative Example 1

Capacitors were obtained by the same treatment as in Example 1 exceptfor omitting the attachment of a siloxane compound using silicone rubberin Example 1 and evaluated in the same manner as in Example 1. Theresults are shown in Table 1.

Comparative Example 2

Capacitors were obtained by the same treatment as in Example 3 exceptfor omitting the attachment of a siloxane compound using silicone rubberin Example 3 and evaluated in the same manner as in Example 3. Theresults are shown in Table 1.

Comparative Example 3

Capacitors were obtained by the same treatment as in Example 4 exceptfor omitting the attachment of a siloxane compound using silicone rubberin Example 4 and evaluated in the same manner as in Example 4. Theresults are shown in Table 1. TABLE 1 Initial Properties Accelerated CDF Humidity Test μF, %, Defective/ Short Defective/ 120 120 LC Sample,Circuited Sample, Hz Hz μA units/units Product units/units Example 1 530.6 0.2 0/30 0 0/30 Example 2 52 0.6 0.2 0/30 0 0/30 Example 3 52 0.60.2 0/30 0 0/30 Example 4 51 0.6 0.2 0/30 0 0/30 Example 5 52 0.6 0.20/30 0 0/30 Example 6 52 0.6 0.2 0/30 0 0/30 Example 7 52 0.6 0.2 0/30 00/30 Example 8 52 0.6 0.2 0/30 0 0/30 Example 9 52 0.6 0.2 0/30 0 0/30Comparative 48 0.7 0.2 0/30 0 5/30 Example 1 Comparative 48 0.7 0.2 0/300 4/30 Example 2 Comparative 47 0.7 0.2 0/30 0 6/30 Example 3

According to the present invention, a compound containing a siloxanebond is attached onto an electrode comprising a valve-acting metalhaving on the surface a fine porous dielectric film so that anelectrolytic capacitor, particularly a solid electrolytic capacitor,with improved adhesion between the dielectric film and the electricallyconducting polymer provides a large capacitance and good reliabilityunder high temperature and high humidity conditions, can be obtained.

Furthermore, a compact and high-performance electrolytic capacitorimproved in high frequency properties and tan δ and exhibiting lowimpedance can be obtained.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A method for manufacturing an electrode for an electrolyticcapacitor, comprising first exposing an electrode comprising avalve-acting metal having on a surface thereof a porous inorganicdielectric film to an ambient atmosphere of a compound having a siloxanebond to substantially attach said compound into fine pores of thedielectric film, and then forming a layer of an electrolyte comprisingan electrically conducting polymer on the dielectric film havingsubstantially attached thereto the compound having a siloxane bond.
 2. Amethod for manufacturing an electrolytic capacitor, comprising: using anelectrode comprising a valve-acting metal having on a surface thereof aporous dielectric film, with an end part thereof undertaking an anodepart, attaching a compound having a siloxane bond onto the dielectricfilm of said electrode, forming in sequence an electrode on thedielectric film and forming further thereon an electrically conductinglayer, thereby fabricating a capacitor device using these members as acathode part, and connecting a lead frame to the anode part and thecathode part, wherein the compound having a siloxane bond is firstsubstantially attached into fine pores of the dielectric film, a layerof an electrolyte comprising an electrically conducting polymer is thenformed on the dielectric film having substantially attached thereto thecompound having a siloxane bond, and the step of substantially attachingthe compound having a siloxane bond into fine pores of the dielectricfilm consists of substantially attaching the compound having a siloxanebond into fine pores of the dielectric film.